Heat gun



JD- 27 1970 F. E. SCHUMACHER 3,492,462

HEAT GUN Filed Oct. 5. 1966 United States Patent C) 3,492,462 HEAT GUN Fred E. Schumacher, 3712 Rio Vista Road, Racine, Wis. 53404 Filed Oct. 3, 1966, Ser. No. 583,518 Int. Cl. F24h 3/04; H05b 3/16 U.S. Cl. 219-370 6 Claims ABSTRACT F THE DISCLOSURE This invention relates to electrical appliances, and more particularly to a device for producing a stream of hot air.

In the prior art, such a device is frequently called a hot air gun or a heat gun. Such a device is called a gun because it often has the appearance of a sidearm or hand gun such as a pistol or revolver and it more or less shoots out hot air. That is, the device has a barrel and a handle grip fixed relative to the barrel. The barrel has an open forward end out of which hot air is blown.

It is conventional to establish a current of air over an electrical heating element by a blower including an electric motor. Both blower and heating element are often supplied with electric current through a switch actuable by a trigger in the handle grip.

Heat guns have been used for many purposes in the past. For example, they have been used to heat plastic to shape it. They have been used as hair driers in beauty salons and the like. They have also been used in removing paint, in Vulcanizing a repair area of a pneumatic tire, and in softening power transmission crank case grease and oil for maintenance or starting.

As indicated previously, heat guns are not unknown in the prior art. For example, some are shown in the following U.S. patents.

Apparatus for Removing Paint, C. H. Kenney, 1,955,240,

Apr. 17, 1934.

Hot Air Gun, A. F. Levenhagen, 2,042,264, May 27,

Apparatus for Vulcanizing a Repair Area of a Pneumatic Tire, L. F. Borda et al., 2,609,477, Sept. 2, 1952.

Electric Paint Removing Device, E. W. Ferris, 3,094,606,

June 18, 1963.

Notwithstanding the fact that several different heat guns have been employed in the prior art, all of such guns have suffered from several serious disadvantages.

Frequently a heating element is wound around the barrel of a heat gun. However, the windings often develop hot spots. Localized heating then can cause the winding to burn out early. The short life of the winding in this case increases the maintenance cost of the gun. Further, the hot spots are due to an inferior arrangement to dissipate the heat generated in the winding. This, in turn, reduces the efficiency of the gun in heating a maximum amount of air to a maximum temperature with a minimum amount of electrical power.

In accordance with the device of the present invention, the above-described and other disadvantages of the prior art are overcome by providing a heat gun including a supporting insulator having an opening therethrough, and a 3,492,462 Patented Jan. 27, 1970 heating element. A blower may then be employed to cirlator may be a barrel made of a ceramic or other insulating material adapted to hold a resistance wire or other heating element. A blower may then be employed to circulate air over the heating element. A blower may then be employed to circulate air over the heating element, through the barrel opening and out the end of the barrel. Thus, by circulating air over the portion of the heating element whch is stretched across the barrel opening, the development of hot spots and localized areas along the heating element is prevented. The heating element therefore does not burn out soon. Its useful life is therefore lengthened and the maintenance cost of the gun is minimized. The use of the construction of the heating element in the position stretched across the barrel opening provides a superior arrangement to dissipate the heat generated in the heating element and to transfer it to the air passing around the heating element and through the barrel opening. The efficiency of the gun in the heat transfer from the heating element to the air is thus kept at a maximum value.

In accordance with another feature of the present invention, a housing having rearward and forward openings is employed. Means are then provided which are xed relative to the housing supporting the heating element in the housing at the forward end of it. The blower is then fixed in the housing at the rearward end thereof. The blower has a motor positioned between the rearward opening in the housing and the heating element. The motor is provided with an output shaft on which a fan blade assembly is fixed. The fan `blade assembly is fixed to the motor output shaft in a position to draw air into the housing through the rearward opening into it. The fan blade assembly also circulates the air forwardly inside the housing in contact with the motor to cool the motor. The air is then circulated over the heating element and exhausted from the housing out of the forward opening therein. Thus, in accordance with the device of the present invention, a small electric motor can be used because it is air cooled by its on action in rotating the fan blade assembly on its output shaft. Further, the circulation of air over the motor and subsequently over the heating element establishes an air current which effectively isolates the motor from the heat produced by the heating element. The motor therefore cannot overheat due to the heat produced by the heating element. It is. an outstanding feature of the device of the present invention that a pressurized air chamber is provided around the barrel inside the housing. Further, the open end of the barrel is made sufficiently large so as to reduce the air ow resistance thereof below the air iiow resistance of any and all heating element openings through the barrel. These arrangements make it possible to keep a positive flow of air through each heating element hole in the barrel. That is, an adequate flow of air is produced through each such hole. No such hole fails to receive an adequate air flow. This desirable air ow thus prevents the development of hot spots on the heating element.

The above-described and other advantages of the present invention will be better understood from the following description when considered in connection with the accompanying drawings.

In the drawings which are to be regarded as merely illustrative:

FIG. 1 is a side elevational View, partly in section, of a heat gun constructed in accordance with one embodiment of the present invention;

FIG. 2 is a rear elevational view of a portion of the heat gun taken on the line 2 2 shown in FIG. l;

FIG. 3 is a transverse sectional view of a portion of the heat gun taken on the line 3 3 shown in FIG. l; and

FIG. 4 is a transverse sectional view of a portion of the barrel of the gun Shown in FIG. 1.

The heat gun of the present invention is indicated at in FIG. 1. Gun 10 has a handle grip 11 and a housing 12. Handle grip 11 is made up of two parts 13 and 14. Housing 12 is made up of two parts 15 and 16. Parts 13 and 14 are separate from each other and are fixed together by conventional means. The same is true of parts 15 and 16. Note will be taken that parts 13 and 15 are integral with one another. The same is true of parts 14 and 16. Parts 15 and 16 may be held together by pins 17, 18, 19, 20, 21 and 22 shown in FIG. 1.

As shown in FIGS. 1 and 3, handle grip 11 has a trigger 23. Trigger 23, handle grip 11, and its entire construction including the component parts of the gun 10 therein and electric cord 24 having wires 25 and 26 thereto may be conventional.

Heat gun 10 includes a heating element 27 and a blower 28. Blower 28 has a motor 29 and a fan blade assembly 30, Motor 29 has an output shaft 31. Fan blade assembly 30 is xed to the right end of the output shaft 31, as shown in FIG. l, between motor 29 and heating element 27 A switch, not shown, may be provided in handle grip 11. The said switch may then be operated by trigger 23 to supply current to heating element 27 and to motor 29 simultaneously. Alternatively, time delay relays or thermal or other time delay devices may be provided to supply electric current to heating element 27 for a predetermined period before motor 29 is energized. Further, such a delay device may also be employed to continue to energize motor 29 after electric current to heating element 27 has been turned off.

By supplying current to heating element 27 before motor 29 is energized, it is possible to supply hot air from the right end of the gun 10 more quickly than it would be possible to do were heating element 27 and motor 29 energized at exactly the same time.

Further, the useful life of heating element 27 may be lengthened by cooling heating element 27 for a brief period of time after electric current thereto has been shut off. Such cooling may also prevent hot spots from developing.

As shown in FIGS. l and 2, housing 12 has rearward openings 32, 33, 34 and 35 from the exterior thereof into the interior thereof. Housing 12 also has a forward opening 36. A barrel 37 is provided in housing 12. Barrel 37 has a closed rearward end 38, and an open forward end 39. Forward end 39 is located in the mouth of forward opening 36 in housing 12.

Barrel 37 is cylindrical. It has a helical rib 40 between the turns of which a helical groove 41 is dened. Helical groove 41 has a semi-circular cross section.

Note will be taken from FIG. 4 that heating element 27 is a helically coiled resistance wire conductor, the axis of which is, in fact, also formed in a helix around barrel 37. The radius of the cross section of groove 41 thus is approximately equal to the radius of each turn of heating element 27. The turn of heating element 27 last referred to is one of the small turns about its own axis rather than one turn thereof about the axis of barrel Barrel 37 has a plurality of holes 42 which extend completely through the cylindrical wall thereof at the position of groove 41 therein. Holes 42 are equally spaced along the general helical path of groove 41. For clarity, the section of barrel 37 shown in FIG. l has been taken precisely at a set of holes at the top and bottom of the barrel wall, as shown in FIG. l. The ends of heating element 27 are indicated at 43 and 44.'Ends 43 and 44 extend through an opening 45 in housing 12 down to a position inside of handle grip 11.

Barrel 37 is supported in housing 12 by ribs 46, 47, 48 and 49 molded integrally with parts 15 and 16 of housing 12. Barrel 37 has a circular disc 60 integral therewith that tits between ribs 48 and 49. Disc 60 therefore not only holds barrel 37 in position in housing opening 36, but disc 60', by being solid, also forces any air in housing 60 blown into the space between barrel 37 and housing 12 over the portions of heating element 27 that are stretched across holes 42 through barrel 37. In other words, it is not possible for air forced into the space between barrel 37 and housing 12 to escape from gun 10 except through barrel holes 42 and out the open end 39 of barrel 37. The motion of air from the space inbetween barrel 37 and housing 12 to the space inside barrel 37 over heating element 27 and through holes 42 is indicated by arrows 61 in FIG. 4.

The position of barrel 37 inside housing 12 is steadied still further by a spider 62 including legs or projections 63 and 64 which t into the space between ribs 46 and 47 of housing 12. The space around barrel 37 between projections 63 and 64 is left vacant so that fan blade assembly 30 can draw air through housing rearward openings 32, 33, 34 and 35 over motor 29 and blow the same air over the outside of barrel 37 around projections 63 and 64 into the space between barrel 37 and housing 12 rearward of disc 60. In this regard, parts 15 and 16 of housing 12 may be identical.

Motor 29 is mounted in housing 12 by screws 50, 51, 52 and 53. Electric motor 29 has electric leads 54 and 55 which extend therefrom through openings 56 and 57 in housing 12 down into the space inside handle grip 11.

Note will be taken that motor 29 is mounted between rearward housing openings 32, 33, 34 and 35 and heating element 27. Further, motor 29 is mounted in a position centrally of housing 12 so that space, for example, at 58 and 59 exists between the outer periphery of motor 29 and the internal surface of housing 12.

In the operation of the heat gun 10y of the present invention, trigger 23 is depressed, and motor 29 is energized. Electric current is then also supplied to heating element 27. Fan blade assembly 30 then begins to turn to the right as viewed in FIG. 3. Fan blade assembly 30 then draws air in through rearward openings 32, 33, 34 and 35 of housing 12, around motor 29 in the space indicated at 58 and 59, around spider projections 63 and 64, forward of projections 63 and 64 between them and disc 60 and into the space between the internal surface of housing 12 and the external surface of barrel 37 thereat. This air is then directed through those portions of the turns of heating element 27 spanning the gaps across barrel holes 42 and through the holes 42 into the interior of the barrel 37. The air is then directed outwardly of the forward open end 39 of barrel 37.

In the prior art, barrels were employed to support heating elements around them. However, a heating element was not supported anywhere near the barrel holes, such as barrel holes 42. Hot spots then developed. Such would be the case with the heat gun 10 of the present invention were not heating element 27 stretched across holes 42 in barrel 37. This is especially true of those remote turns rlocated nearest to disc 60 where it is most dicult to establish a strong current of air and thereby effect a rapid transfer of heat from heating element 27 to keep heating element 27 cool. This difficulty is encountered because the said remote turns are fartherest from fan blade assembly 30 and are effectively boxed in between barrel 37 and housing 12.

Note will be taken that the air passing through housing l 12 of motor 29 not only cools the motor armature and stator, but it also cools the bearings in which output shaft 31 is mounted, although these bearings are not shown. However, motor 29, by itself, may be entirely conventional.

Note will be taken that barrel 37 acts as a partition to prevent air from entering the interior thereof through holes 42 except by the passage of air over heating element 27. Openings into barrel 37 are therefore limited to holes 42 and forward opening 39.

Note will be taken that when housing 12 is put together wlth parts 15 and 16, it is generally hollow, elongated,

and cylindrical. Housing 12 provides an enclosure for heat gun 12 except for rearward openings 32, 33, 34 and 35 and forward opening 36.

Similarly, barrel 37 is a generally hollow, elongated and cylindrical body.

Note will be taken that alternative structures may be employed in accordance with the present invention. Note Will be taken that heating element 27 may be mounted inside of barrel 37. However, it will be appreciated that perhaps the most important form of the invention will utilize heating element 27 on the outside of barrel 37 because it will be possible to mount heating element 27 in this position more easily and in the shortest time with the least possible cost of construction. Further, barrel 37 could be turned end for end and opening 36 could be made larger. In this case, air could emanate from the space inbetween barrel 37 and the internal surface of housing 12 at opening 36.

It is not important precisely what material is used for the conductive wire of heating element 27 and the insulating material of barrel 37.

All the component parts of blower 28 may be conventional. Blower 28 may in fact be entirely conventional except for its mounting in the position shown in FIG. 1 with motor 29 spaced from the internal surface of housing 12.

If it is desired simply to operate motor 29 and heating element 27 simultaneously, it is, of course, possible to do so simply by connecting a double pole, double throw switch to wires 25 and 26 to cord 24 land to corresponding wires 43, 44, 54 and 55 of heating element 27 and motor 29, respectively. The double pole, double throw switch could then be operated by trigger 23. As stated previously, every portion of the construction of the heat gun outside of housing 12 may be entirely conventional, if desired.

Many of the alternative constructions described herein will, of course, simply involve transposition of the cornponent parts of the heat gun 10. They will therefore not depart from the invention as disclosed, or claimed.

From the foregoing, it will be appreciated that by passing air over the turns of heating element 27 spanning the gaps across holes 42 in barrel 37, it is possible to prevent hot spots from being created at any point throughout the winding of heating element 27. This, therefore, increases the length of the useful life of heating element 27. The maintenance cost of the heat gun 10 is therefore maintained at a minimum value. The positive manner in which air is circulated over and around the turns of heating element 27 also increases the efliciency of transferring heat from heating element 27 to the air.

It is also an advantage of the present invention that a small motor may be used and cooled effectively by employing the arrangement of heat gun 10 where air is drawn through rearward openings 32, 33, 34 and 3S over motor 29 and eventually exhausted from heat gun 10 to keep motor 29 cool as hot air is expelled from openings 36 and 39 at the forward end of heat gun 10 through the forward ends of housing 12 and "barrel 37.

Note will be taken that the space inside housing 12 between the cylindrical wall thereof and the external surface of barrel 37 is pressurized when motor 29 is energized. The open end 39 of barrel 37 is made sufliciently large so that the air flow resistance at the open end at 39 is less than the air flow resistance of holes 42. This condition may be approxima-tely maintained by making the total area of all of the holes 42 no greater than the area of end 39. This means that air under pressure is maintained in housing 12 outside of 'barrel 37 at each of the holes 42 so that air is in fact forced through each one of 'holes 42 and a circulation of air is not omitted through any one of the holes 42. This therefore prevents hot spots from forming on heating element 27.

If desired, the helical turns of heating element 27 may terminate abruptly at the positions of the end holes of the helical series of holes 42. This termination of the coiled ends of heating element 27 may thus effectively prevent hot spots from forming on the ends of heating element 27. Thus, ends 43 and 44 of heating element 27 will have a relatively low resistance whereas the helical turns of heating element 27 may have a relatively high resistance.

What is meant by the air ow resis-tance of the open end 39 of barrel 37 is the unimpeded air flow resistance. That is, note will be taken if the open end 39 of barrel 37 is closed tightly, no circulation of air can take place either through open end 39 or through holes 42. Thus, each heat gun made in accordance with the present invention ought to have instructions as to the appropriate distance the open end 39 of barrel 37 should be kept from the work to be heated by the heat gun.

Note will be taken that the relative air ow resistance of barrel end 39 and holes 42 make it possible to keep a positive flow of air through each hole 42.

Note will be taken that it i-s an outstanding feature of the invention that the above-mentioned relative air flow resistances are maintained. This feature of the invention therefore may be used without the feature of the invention including the heating element 27 extending across holes 42. Alternatively, the feature of the position of heating element 27 across holes 42 may be employed without the feature including the specific air flow resistance relation. In addition, as shown, both of these features of the invention may be employed together.

It is also a feature of the invention that the forward portion of housing 12 and barrel 37 may be made independently of the remainder of the heat gun 10. That portion of the housing 12 and barrel 37 may have a quick detachable connection to the remainder of heat gun 10, if desired. In that case, a quick detachable helical connector will have to be provided for the ends of heating element 27. The present invention therefore comprehends the said portion of the gun 10 independently as well as in combination with the remainder of the gun. The use of a separate housing portion and barrel could be made in order to accomplish several ends. The first might be the use of different housing, barrel and heating element designs for different temperatures. Maintenance or service and part replacement could also be made easier with the use of this construction.

Although only one specific embodiment of the present invention has -been described and illustrated herein, many changes and modifications will of course suggest themselves to those skilled in the art. This single embodiment has been selected for this disclosure for the purpose of illustration only. The present invention should therefore not be limited to the embodiment so selected, the true scope of the invention being defined only in `the appended claims.

What is claimed is:

1. A heat gun comprising: a hollow, elongated, cylindrical, enclosed housing constructed of two assembled parts having rearward and forward openings extending from the exterior thereof into the interior thereof; a 4blower mounted inside the rearward end of said housing adjacent said rearward opening, said blower having a cylindrical motor mounted in said housing in a position spaced from the internal Iwalls thereof; a hollow, elongated, cylindrical barrel of insulative material in the forward end of said housing, said barrel having an outside diameter Smaller than the inside diameter of Said housing, said barrel having an open forward end and a rearward end closed by an imperforate wall, said barrel having a spider integral therewith at its rearward end, said spider having radially spaced legs to hold said barrel in spaced relation to the internal surface of said housing; ribs carried by the housing for receiving the spider therewithin; means at the forward end of said barrel closing off the space between said barrel and said housing, the open end of said barrel being positioned within the forward opening in said housing, said barrel having a helical rib therearound, said rib having spaced turns, a helical groove in the external surface of said barrel defined between the turns of said helical rib, said groove having a semicircular cross section; a heating element including an open coil wire conductor having spaced turns in said groove, said conductor being approximately in the shape of a helix, the axis of said conductor helix itself being in the shape of a helix, the outer radius of the said conductor helix turns being approximately equal to the radius of curvature of the cross section of said groove, said barrel having a series of spaced holes therethrough at the bottom of said groove, said blower being adapted to pressurize the space between said barrel and said housing, the unimpeded air flow resistance of the open end of said barrel being less than the air flow resistance of said holes; and means to pass electric current to said motor and said heating element, said motor having an output shaft extending longitudinally in said housing, said blower including a fan blade assembly fixed to said shaft to draw air into said housing through said rearward opening and to establish a current of said air radially inward into said barrel through the turns of said heating element which span the gaps across said holes in said barrel and through said holes and out of said open end of said barrel.

2. The invention as defined in Claim 1, wherein the total area of all of said holes is no greater than the area of the open end of said barrel.

3. A heat gun comprising: a housing having rearward and forward openings extending from the exterior thereof into the interior thereof; a barrel in said housing, said barrel having one open end facing generally toward the housing forward opening and one closed end facing generally toward the housing rearward opening; a hole through the wall of said barrel; a heating element including a conductor lying outwardly of the barrel within the space between the barrel and the housing and stretched across said hole; means interrelating the barrel and housing forwardly of the hole in said barrel for restricting air ow between said barrel and housing outwardly of the forward opening; and means to establish a current of air (l) into said housing through said rearward opening, (2) over the portion of said conductor stretched across said hole, (3) through said hole, and (4) outwardly of said barrel open end and said housing through said forward opening.

4. A heat gun comprising: a housing having a forward opening extending from the exterior thereof into the interior thereof; a hollow insulative body in said housing, said body providing an enclosed space except for a plurality of holes therethrough arranged in a helical path and one open end, said open end being located in said forward housing opening, said body being mounted centrally in said housing, said mounting means being constructed to allow air to iiow between the outside of said body and said housing, said body having an external surface spaced from the internal surface of said housing; means closing off the space between said body and said housing adjacent the forward ends thereof; a heating element including a conductor helically wound onto the external surface of said body in a position stretched across and spanning the gaps across said holes whereby said conductor has intermittently spaced portions lying in opposed condition to said openings; said housing including inlet means; a blower fixed to said housing in a position to circulate air (1) through said inlet means forwardly between said housing and said body, (2) over those portions of said heating element spanning the gaps across said holes, (3) through said holes, and (4) out the said open end of said body, said blower including an electric motor; and means to supply electric current to said heating element and to said motor.

5. A heat gun comprising: a housing having a forward opening extending from the exterior thereof into the interior thereof; an inlet means for said housing; a barrel of insulative material in said housing having a hollow, elongated, cylindrical wall, said barrel having one open end and one closed end, said barrel having a plurality of holes extending through the said wall of said barrel, said open end being located in said forward housing opening, said barrel being mounted centrally in said housing, said mounting means being constructed to allow air to iiow between said barrel and said housing, said barrel having an external surface spaced from the internal surface of said housing; means closing off the space between said barrel and said housing adjacent the forward ends thereof; a heating element including a conductor wound onto the external surface of the cylindrical wall of said barrel in a helical path about said wall and in a position stretched across and spanning the gaps across said holes, said conductor being an open coil helix having an axis which itself is shaped into a helix about the symmetrical axis of said cylindrical barrel wall; a blower fixed to said housing in a position to circulate air (1) through the inlet means and forwardly between said housing and said barrel, (2) over those portions of said heating element spanning the gaps across said holes, (3) through said holes, and (4) out the said open end of said barrel, said blower including an electric motor; and means to supply electric current to said heating element and to said motor.

6. In apparatus for directing a confined pressurized stream of highly heated air along a substantially straightline path having an electric fan for generating a supply of pressurized air, and air heating and directing means, the improvement comprising: said heating and directing means including an elongated tube having an imperforate closed end and an open end, the side wall of said tube including a plurality of spaced openings arranged in a generally helical path and the outer wall surface of said tube formed into a continuous helical groove coextensive with the path of said openings and lying in opposed relation thereto; housing walls in surrounding relationship to the tube side rwall spaced from said side wall to form an enclosure about the portion of the tube including the openings, said housing Wall being imperforate except for at least one inlet opening adjacent the closed end of the tube through which the supply of pressurized air from said fan is injected; and an electric heating element lying within the tube groove whereby on providing electric current to the element the pressurized air moving into the space between the housing wall and tube wall passes over and about the heating element to enter the interior of the tube solely through the tube openings forming a highly heated pressurized air stream that is emitted from the open end of the tube along the straight-line path.

References Cited UNITED STATES PATENTS 783,057 2/1905 Mahoney 219-374 X 1,446,703 2/ 1923 Hnilo 219-367 X 1,534,682 4/1925 Carmean et al. 219-377 X 2,031,391 2/1936 Spielnian 219-370 X 2,042,264 5/ 1936 Levenhagen 219-375 X 2,491,399 12'/ 1949 Thompson 219-37'0 3,094,606 V6/1963 Ferris 219-370 X 3,261,107 7/1966 Ponczek et al. 219-370 FOREIGN PATENTS 545,801 3/ 1932 Germany.

547,221 3/ 1932 Germany.

ANTHONY BARTIS, Primary Examiner U.S. Cl. X.R. 219-368, 373, 374 

